Venous thrombosis is a condition in which a blood clot (thrombus) forms in a vein. This clot can limit blood flow through the vein, causing swelling and pain. Most commonly, venous thrombosis occurs in the "deep veins" in the legs, thighs, or pelvis (figure 1); this is called a deep vein thrombosis, or DVT.

DVT is the most common type of venous thrombosis. However, a thrombus can form anywhere in the venous system. If a part or all of the blood clot in the vein breaks off from the site where it is formed, it can travel through the venous system; this is called an embolus. If the embolus lodges in the lung, it is called pulmonary embolism (PE), a serious condition that leads to over 50,000 deaths a year in the United States. In most cases, PE is caused when part of a DVT breaks off and lodges in the lung. The term "venous thromboembolism" is sometimes used when discussing both DVT and PE.

There are a number of factors that increase a person's risk of developing a deep vein thrombosis.

If a person is found to have a DVT and there is no known medical condition or recent surgery that could have caused the DVT, it is possible that an inherited condition is the cause. This is especially true in people with a family member who has also experienced a DVT or pulmonary embolism. In these cases, testing for an inherited thrombophilia may be recommended. However, finding an inherited thrombophilia does not change the way that doctors treat the venous thromboembolism, and may not increase the chance of the blood clot coming back. (See 'Finding the cause of venous thrombosis' below.)

Elevated clotting factors — Having an increased level of one or more factors involved in blood clotting, such as factor VIII, increases the risk of a blood clot.

Medical conditions or medications — Some medical conditions and medications increase a person's risk of developing a blood clot:

●Pregnancy

●Obesity

●Smoking

●Heart failure

●Previous DVT or PE

●Increased age

●Cancer — Some cancers increase substances in the blood that cause blood to clot.

●Certain medications (eg, birth control pills, hormone replacement therapy, erythropoietin, tamoxifen, thalidomide). The risk of a blood clot is further increased in people who use one of these medications, and also smoke or are obese.

Surgery and related conditions — Surgical procedures, especially those involving the hip, pelvis, or knee, increase a person's risk of developing a blood clot. During the recovery period, this risk often continues because the person is less active. Inactivity during long trips can also increase a person's risk of developing a blood clot. Precautions to reduce the risk of blood clots are discussed below (see 'Deep vein thrombosis prevention' below).

●Major surgery (especially orthopedic surgery and neurosurgery)

●Trauma, especially if blood vessels are injured

●Prolonged sitting, especially sitting for six or more hours on a plane, or bed rest

Acquired thrombophilia — Some types of thrombophilia are not inherited, but can still increase a person's risk of developing a blood clot.

●Certain disorders of the blood, such as polycythemia vera or essential thrombocythemia

Inherited thrombophilia — Inherited thrombophilia refers to a genetic problem that causes the blood to clot more easily than normal. Various factors in the blood clotting process may be involved, depending on the type of genetic problem present.

An inherited thrombophilia is occasionally present in people with a venous blood clot (ie, thrombus). For example, deficiencies of antithrombin, protein C, or protein S can be found in less than 5 percent of patients who have had an unprovoked venous blood clot (a blood clot not caused by a medical or surgical condition). Other factors, such as factor V Leiden or the prothrombin gene mutation, can occur in approximately 20 to 25 percent of people with a venous blood clot. However, factor V Leiden or the prothrombin gene mutation is also found in up to 5 percent of otherwise healthy Caucasians. Venous thrombosis is infrequent before adolescence in people with inherited thrombophilia.

DEEP VEIN THROMBOSIS SYMPTOMS

The signs and symptoms of DVT may be caused by a clot, or may be related to another condition. Imaging studies are needed to determine if a clot is present.

Superficial phlebitis — Superficial phlebitis (SP) causes pain, tenderness, firmness, and/or redness in a vein due to inflammation, infection, and/or a blood clot (thrombus). It is most commonly seen in the inner part of the lower legs.

Superficial phlebitis differs from a deep vein thrombosis because the veins that are affected are near the surface of the skin. Symptoms of SP typically develop over hours to days and resolve in days to weeks. The area may continue to be firm for several weeks to months. Treatment usually includes warm or cool compresses, elevation of the leg, a non-steroidal antiinflammatory agent (NSAID) such as ibuprofen (Advil, Motrin), or anticoagulation. In most people with SP, there is a low risk of developing a DVT or pulmonary embolism, so anticoagulation is not usually needed.

D-dimer — D-dimer is a substance in the blood that is often increased in people with DVT or PE. D-dimer testing is sometimes useful for patients with a suspected DVT or PE. If the D-dimer test is negative and the patient has a low risk of DVT or PE based upon his/her history and physical examination, DVT or PE are unlikely and further diagnostic testing may not be needed.

Compression ultrasonography — Compression ultrasonography uses sound waves to generate pictures of the structures inside the leg. For this type of exam, a person lies on his/her back and then stomach as an ultrasound wand is applied to the leg. In most circumstances, compression ultrasonography is the test of choice for patients with suspected DVT.

Contrast venography — During contrast venography, a catheter is threaded into a vein and a dye is injected. This allows the clinician to see the vein with x-ray. Venography is generally reserved for situations in which ultrasound cannot be done, when other tests have not been helpful, or when other tests are negative but the clinician feels strongly that a venous thrombosis is present.

Magnetic resonance imaging (MRI) — MRI uses a strong magnet to produce detailed pictures of the inside of the body. MRI is as accurate as contrast venography. MRI is expensive, and its use may be limited to situations in which contrast venography cannot be performed, such as in patients with poor kidney function, during pregnancy, or because of allergy to the dye required in contrast venography.

Finding the cause of venous thrombosis — After determining that DVT or PE is present, the healthcare provider will want to know what caused it. In many cases, there are obvious risk factors such as recent surgery or immobility. (See 'Acquired thrombophilia' above.) In other cases, the clinician may test for the presence of an inherited form of thrombophilia or for another medical condition associated with an increased risk for venous thrombosis. (See 'Inherited thrombophilia' above.)

Persons with some acquired or inherited abnormalities may require additional treatment or prevention measures to reduce the risk of another thrombosis. Some experts recommend that the family members of a person with an inherited thrombophilia be screened for the inherited condition if this information would affect their care as well, although this issue is controversial. It is important that the healthcare provider discusses the pros and cons of screening for an inherited thrombophilia with the patient before this testing is done.

DEEP VEIN THROMBOSIS TREATMENT

The treatment of DVT and PE are similar. In DVT, the main goal of treatment is to prevent a PE. Other goals of treatment include preventing the clot from becoming larger, preventing new blood clots from forming, and preventing long-term complications of PE or DVT.

The primary treatment for venous thrombosis is anticoagulation. Other available treatments, which may be used in specific situations, include thrombolytic therapy or placing a filter in a major blood vessel (the inferior vena cava).

Anticoagulation — Anticoagulants are medications that are commonly called "blood thinners". These medications do not actually thin the blood, but rather helps to prevent new blood clots from forming. Patients with venous thrombosis are usually treated first with an injectable anticoagulant. There are several such anticoagulants available, including:

These agents can all be injected under the skin (ie, subcutaneous injection) by the patient, a family member, or a home health nurse. This allows selected patients to be treated at home. Heparin, low molecular weight heparin, or fondaparinux are usually continued for at least five days, along with another medication called warfarin (Coumadin). Warfarin is a pill that is taken by mouth. After approximately five days, the heparin, low molecular weight heparin or fondaparinux are discontinued while the warfarin is continued for at least three months.

Less commonly, the patient does not take warfarin or any of the target-specific oral anticoagulants but takes a daily injection of low molecular weight heparin or fondaparinux for the entire treatment period. Low molecular weight heparin, fondaparinux, and the target specific oral anticoagulants (eg, rivaroxaban) are more expensive than warfarin, but they do not need to be monitored with blood clotting tests.

For patients taking warfarin, the clotting factors in the blood need to be measured on a regular basis with a blood test called the International Normalized Ratio (INR). The target level INR for people on warfarin is usually between 2 and 3. (See "Patient information: Warfarin (Coumadin) (Beyond the Basics)".)

The choice of anticoagulant usually depends upon the preference of the patient and the healthcare provider, the patient's medical condition, and cost issues.

Duration of treatment — Anticoagulation is recommended for a MINIMUM of three months in a patient with DVT.

●In patients who had a reversible risk factor contributing to their DVT, such as trauma, surgery, cancer, or being confined to bed for a prolonged period, the person is often treated with anticoagulation for three months or until the risk factor is resolved.

●Expert groups recommend that people who develop a venous thrombosis and who do not have a known risk factor for thrombosis be treated with an anticoagulant for an indefinite period of time [1]. However, this decision should be discussed with the person's healthcare provider after three months of treatment, and then reassessed on a regular basis. Some people prefer to continue the anticoagulant, which may carry an increased risk of bleeding, while others prefer to stop the anticoagulant at some point, which may carry an increased risk for repeat thrombosis.

●People who have an underlying medical risk factor for thrombosis, such as the antiphospholipid syndrome, are advised to continue anticoagulation indefinitely after a first spontaneous DVT or PE.

●Most experts recommend continuing anticoagulation indefinitely for people with two or more episodes of venous thrombosis or if a permanent risk factor for clotting is present (eg, a mechanical heart valve).

Walking during DVT treatment — Once an anticoagulant has been started and symptoms (eg, pain, swelling) are under control, the person is strongly encouraged to get up and walk around. Studies show that there is no increased risk of complications (eg, pulmonary embolus) in people who get up and walk, and walking may in fact help the person feel better faster.

Thrombolytic therapy — In some cases, a healthcare provider will recommend an intravenous medicine to dissolve blood clots. This is called thrombolytic therapy. This therapy is reserved for patients who have serious complications related to PE or DVT, and who have a low risk of serious bleeding as a side effect of the therapy. The response to thrombolytic therapy is best when there is a short time between the diagnosis of DVT/PE and the start of thrombolytic therapy.

Inferior vena cava filter — An inferior vena cava (IVC) filter is a device that blocks the circulation of clots in the bloodstream. It is placed in the inferior vena cava (the large vein leading from the lower body to the heart). The IVC filter typically is inserted through a small incision in a neck vein with the use of a local anesthetic and takes 20 to 30 minutes to perform. An IVC filter is often recommended in patients with venous thromboembolism who cannot use anticoagulants because of a very high bleeding risk.

Use of an IVC filter may be recommended in patients with pulmonary problems due to chronic recurrent embolism, although this is controversial. In the long term, IVC filters can increase the risk of developing blood clots.

DEEP VEIN THROMBOSIS PREVENTION

Surgical patients — Certain high risk patients undergoing surgery (especially bone or joint surgery and cancer surgery) may be given anticoagulants to decrease the risk of blood clots. Anticoagulants may also be given to women at high risk for venous thrombosis during and after pregnancy.

In surgical patients with a moderate to low risk of blood clots, other preventive measures may be used. For example, some surgical patients are fitted with inflatable compression devices that are worn around the legs during and immediately after surgery and periodically fill with air. These devices apply gentle pressure to improve circulation and help prevent clots.

Graduated compression stockings may also be recommended; these stockings apply pressure to the lower legs, with the greatest pressure at the ankle. The pressure gradually decreases up to the knee. For all patients, walking as soon as possible after surgery can decrease the risk of a blood clot.

Extended travel — Prolonged travel appears to confer a two- to fourfold increase in risk of venous thromboembolism (VTE) [2]. There are a few tips that may be of benefit during extended travel (table 1).

SPECIAL PRECAUTIONS FOR PEOPLE WITH DEEP VEIN THROMBOSIS

Second thrombosis — Patients being treated for venous thrombosis are at an increased risk for developing another blood clot, although this risk is significantly smaller when an anticoagulant is used. The patient should watch for new leg pain, swelling, and/or redness. If these symptoms occur, the patient should speak to his/her healthcare provider or seek medical attention as soon as possible.

Other symptoms may indicate that a clot in the leg has broken off and traveled to the lung, causing a pulmonary embolism. These may include:

●New chest pain with difficulty breathing

●A rapid heart rate and/or a feeling of passing out

This complication may be life-threatening and requires immediate attention. Emergency medical services are available in most areas of the United States by calling 911.

Bleeding — Anticoagulants such as heparin and warfarin can have serious side effects and should be taken exactly as directed. If a dose is forgotten, the patient should call his/her provider or clinic for advice. The dose should not be changed to make up for missed doses, unless the provider or clinic directs the patient to do so. Patients should immediately report to the pharmacist or physician if the pill or tablet looks different from the previous bottle. Other precautions are necessary when taking warfarin, and are outlined in a separate topic review. (See "Patient information: Warfarin (Coumadin) (Beyond the Basics)".)

Patients may bleed easily while taking anticoagulants. Bleeding may develop in many areas, such as the nose or gums, excessive menstrual bleeding, bleeding in the urine or feces, bleeding or excessive bruising in the skin, as well as vomiting material that is bright red or dark brown like coffee grounds. In some cases, bleeding can develop inside the body and not be noticed immediately. Bleeding inside the body can cause a person to feel faint, or have pain in the back or abdomen. A healthcare provider should be notified immediately if there is any sign of this problem. A healthcare provider should also be notified immediately if the patient on anticoagulants sustained an injury that could lead to bleeding inside the body.

Wear an alert tag — People who take anticoagulants should wear a bracelet, necklace, or similar alert tag at all times. If medical treatment is required and the person is too ill to explain his/her condition, the tag will alert responders about the patient's use of anticoagulants and risk of excessive bleeding.

The alert tag should list the person's medical conditions, as well as the name and phone number of an emergency contact. One device, Medic Alert, provides a toll-free number that emergency medical workers can call to find out a person's medical history, list of medications, family emergency contact numbers, and healthcare provider names and numbers.

Reduce the risk of bleeding — Some simple modifications can limit the risk of bleeding:

●Use a soft bristle toothbrush

●Shave with an electric razor rather than a blade

●Take care when using scissors or knives

●Avoid potentially harmful activities (eg, contact sports)

●Do not take aspirin or other NSAIDS (eg, ibuprofen, Advil, Aleve, Motrin, Nuprin) unless directed to do so by a healthcare provider. Other nonprescription pain medications, such as acetaminophen, may be a safe alternative.

WHERE TO GET MORE INFORMATION

Your healthcare provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed on our website (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.

The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.

Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.

Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.